title: Characterization of soybean β-expansin genes and their expression responses to symbiosis, nutrient deficiency, and hormone treatment.
abstract: Expansins are plant cell wall-loosening proteins encoded by a superfamily of genes including α-expansin, β-expansin, expansin-like A, and expansin-like B proteins. They play a variety of biological roles during plant growth and development. Expansin genes have been reported in many plant species, and results primarily from graminaceous members indicate that β-expansins are more abundant in monocots than in dicots. Soybean [Glycine max (L.) Merr] is an important legume crop. This work identified nine β-expansin gene family members in soybean (GmEXPBs) that were divided into two distinct classes based on phylogeny and gene structure, with divergence between the two groups occurring more in introns than in exons. A total of 887 hormone-responsive and environmental stress-related putative cis-elements from 188 families were found in the 2-kb upstream region of GmEXPBs. Variations in number and type of cis-elements associated with each gene indicate that the function of these genes is differentially regulated by these signals. Expression analysis confirmed that the family members were ubiquitously, yet differentially expressed in soybean. Responsiveness to nutrient deficiency stresses and regulation by auxin (indole-3-acetic acid) and cytokinin (6-benzylaminopurine) varied among GmEXPBs. In addition, most β-expansin genes were associated with symbiosis of soybean inoculated with Rhizobium or abuscular mycorrhizal fungi (AMF). Taken together, these results systematically investigate the characteristics of the entire GmEXPB family in soybean and comprise the first report analyzing the relationship of GmEXPBs with rhizobial or AMF symbiosis. This information is a valuable step in the process of understanding the expansin protein functions in soybean and opens avenues for continued researches.
authors.affiliation: State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, Root Biology Center, South China Agricultural University, Guangzhou, People's Republic of China.
authors.forename: Xinxin
authors.initials: X
authors.lastname: Li
authors.forename: Jing
authors.initials: J
authors.lastname: Zhao
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Walk
authors.forename: Hong
authors.initials: H
authors.lastname: Liao
mesh_terms: D003583:Cytokinins / Q000378:metabolism; D005502:Food; D020869:Gene Expression Profiling; D023061:Gene Order; D007210:Indoleacetic Acids / Q000378:metabolism; D038821:Mycorrhizae / Q000254:growth & development; D010937:Plant Growth Regulators / Q000378:metabolism*; D010940:Plant Proteins / Q000096:biosynthesis* / Q000235:genetics*; D020218:Response Elements; D012231:Rhizobium / Q000254:growth & development; D017386:Sequence Homology, Amino Acid; D013025:Glycine max / Q000235:genetics / Q000502:physiology*; D013312:Stress, Physiological; D013559:Symbiosis
chemical_list: D003583:Cytokinins; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D010940:Plant Proteins; C095825:expansin protein, plant